The present invention relates generally to lawn mowers and, more particularly, to a lawn mower cutting blade spindle assembly which includes a cutting blade that can withstand impact loading and that can easily be detached from the mower without disturbing the pre-set compression applied to the other components of the spindle assembly.
Conventional lawn mowers utilize a rotatable cutting blade mounted underneath the mower's cutting deck to cut grass, vegetation and the like. Typically in commercial lawn mowers, the cutting blade is attached to the lower end of an elongate spindle shaft that is vertically supported by various bearings and bearing spacers within a spindle housing carried by the mower frame. The upper end of the spindle shaft projects above the spindle housing and has a pulley attached thereto that is configured to receive a drive belt connected to the mower's engine. In operation, the engine activates the drive belt to generate rotation of the pulley, which in turn causes rotation of the spindle shaft, which in turn causes rotation of the cutting blade to thereby cut the grass.
Periodically, the user of such a lawn mower will find it necessary to detach the cutting blade from the mower for the purpose of sharpening the blade, adjusting the height of the cut, or for general maintenance purposes. Therefore, most commercial lawn mowers are designed such that the user can easily detach the cutting blade from the spindle shaft to perform the required maintenance, and then reattach the cutting blade to the spindle shaft after such maintenance has been performed. Preferably, this detachment/reattachment process can be done in the field using ordinary tools.
Some lawn mowers are designed such that the cutting blade is attached to the mower with a short bolt that passes through the cutting blade and into a tapped end of the spindle shaft. The user of the mower can easily detach the cutting blade from the mower by simply unscrewing the short bolt out of the spindle shaft, and can reattach the cutting blade to the mower by screwing the short bolt back into the spindle shaft. One problem with this design, however, is that the short bolt is prone to breakage when the cutting blade encounters thick vegetation, tree branches, stones, or other large objects that can retard or prevent rotation of the cutting blade. Even if the short bolt does not break, the threading in the tapped end of the spindle shaft may become stripped due to the relative movement between the spindle shaft and cutting blade upon impact loading. In either case, damage to the spindle assembly will necessarily result in failure of the lawn mower.
In an attempt to overcome these problems, some lawn mowers have been designed which utilize a longer bolt to attach the cutting blade to the mower. For example, in U.S. Pat. No. 5,782,073 to Sheldon, an elongate bolt passes through the cutting blade and extends upwardly through a longitudinal bore formed on the inside of the spindle shaft. A nut tightened onto the bolt at its upper end is used to attach the cutting blade to the spindle shaft. This longer bolt is not likely to break when the cutting blade strikes a large object. In addition, the nut can be sufficiently tightened onto the threaded upper end of the bolt to prevent relative movement between the cutting blade and spindle shaft upon impact loading.
While use of a longer bolt as disclosed in the Sheldon patent overcomes the problems associated with "short bolt" mowers, it has other shortcomings which can lead to failure of the mower. In particular, the nut that is used to attach the cutting blade to the spindle shaft is also used to compress the pulley and bearing assembly against the spindle shoulder. As such, the compression applied to the pulley and bearing assembly is lost whenever the nut is unscrewed to detach the cutting blade from the spindle shaft. Experience has shown that if the nut is not sufficiently tightened onto the bolt when the cutting blade is reattached to the spindle shaft, the pulley and bearing assembly will become loose and fail due to premature wear. Thus, this mower design is also vulnerable to failure.